We are studying the molecular mechanisms that underlie the formation of axon tracts using a panel of monoclonal antibodies generated against the nervous system of the leech. Some of these antibodies stain sets and subsets of sensory axons while others stain glial cells surrounding these axons. As the sensory axons develop or regenerate, they align themselves with other axons bearing the same antigen. On immunoblots, all of these antibodies react with a group of glycoproteins with the same molecular weight of 130 kD. So far, there is evidence that two of the mabs bind to carbohydrate determinants, which raises the possibility that axonal identity is specified through differentially glycosylating a common core protein. We postulate that these 130 kD glycoproteins play a decisive role in axon tract formation with the neuronal proteins helping to guide sensory afferents into the CNS and the glial cell proteins serving as a generally permissive substrate for axonal growth. We have proposed biochemical, immunochemical and tissue culture experiments to further characterize the proteins p130 and to probe into their function. We are analyzing the protein cores of the 5 different protein p130, isolated so far, using peptide mapping and gel technology. We will also generate new mabs reactive with amino acid epitopes on the proteins p130. These mabs will be used to further characterize the existing proteins and to search for novel proteins, so far as they exist. In tissue culture studies, we will test the impact of both the immunopurified proteins p130 and different mabs against carbohydrate and amino epitopes on axonal growth. We have the tools to address general principles of axon growth relevant to regeneration and development making use of the simple body plan of the leech, a classical invertebrate preparation.